This invention relates to an automatic speed control for seam welding.
Welding machines which utilize either manual setting or a programming device, such as an N/C or tracer control, for directing the welding head along a predetermined path at a set speed, have long been in use. The machines have been used to manufacture relatively large parts such as booms, C-frames and the like, which may include not only straight line segments but also contoured segments.
Many such known welding machines include a transverse beam or bridge which defines a transverse or X axis and which is movable along rails or the like which define a longitudinal or Y axis. A carriage mounted for movement along the bridge carries a metal working tool, such as a welding head or the like.
It is known to mount a sensing means such as a probe adjacent and in advance of the welding head for the purpose of sensing the position of the groove or seam for welding.
Reference is made to copending U.S. patent application Ser. No. 24,696, filed Mar. 28, 1979, entitled "Programmed Welding Machine With Continuously Monitored Override Control" and assigned to the same assignee, for a further explanation of such types of machines.
In the manufacture of C-frames and the like, it is necessary to seam weld a pair of parts together along a groove. The parts are suitably positioned prior to welding, and at least in some instances may be tack welded together to hold them in place. Due to the peculiarities of certain metal parts which are to be assembled by welding, and/or due to irregularities in tack welding and the like, the groove width may not be uniform and may vary randomly throughout its length.
In seam welding using a wire electrode fed at a constant rate, the machine is normally set (either manually or by a suitable program) so that the weld head traverses the groove at a constant speed commensurate with obtaining an adequate weld bead which will firmly join the two metal members. However, if the groove should widen or narrow during this operation, and if the weld head speed remains constant, the quality of the weld will be compromised. With too wide a groove, the bead will not fill the gap and a weak joint will be formed. With too narrow a groove, the weld material will undesirably overflow.
Because each pair of workpieces to be joined are different from any other pair, and because of variations in each tack weld set-up, changes in weld head speed cannot be pre-programmed into the control unit to compensate for random groove width variations. Heretofore, such speed changes have had to be made manually by an operator who had to determine by visual observation the groove width variations.
The invention is particularly adapted for use in connection with welding a pair of metal parts which are positioned to form the welding groove, wherein the positioning is inaccurate and/or one of the parts is uniformly within the desired tolerances and the other part is not.
It is a task of the invention that, when the two parts to be welded are improperly mounted to thereby create a groove of undesirably varying random width, a surface on at least one of the parts is utilized to provide measurement of the groove width deviation.
It is a further task of the invention that, regardless of whether the part positioning is proper or not, when one of the two parts to be welded is uniformly within the desired tolerances and the other part is not, or when both parts are not within the desired tolerances, a surface on at least one of the parts is used in providing the measurement of the groove width deviation.
It is yet another task of the present invention to provide a device which automatically measures random changes in the width of a groove to be seam welded, and which compensates for such changes by changing the speed of the weld head drive mechanism.
It is a further task of the present invention to utilize the main groove position sensing probe and/or an auxiliary sensing device in carrying out the functions of the automatic device.
In accordance with one aspect of the invention, primary and auxiliary sensing probes are provided with the primary probe adapted to lead and control the position of the welding head in its traversing of the groove. The probes are fixedly connected together, with the primary probe adapted to follow a wall of the weld groove formed in one part while the auxiliary probe is adapted to separately engage a surface on the other part.
In accordance with another aspect of the invention, a deviation in the groove width caused by undesirable random variations in said weld groove wall causes the primary probe to move the mounting of the auxiliary probe, thereby creating output signals to change the speed of the weld head drive motor.
In accordance with an additional aspect of the invention, a deviation in groove width caused by an undesirable random variation in the said surface of the other part also causes the auxiliary probe to create an output signal to change the speed of the weld head drive motor.
In accordance with a further aspect of the invention, the primary probe is loaded against the groove wall by electrical balancing circuitry, while the auxiliary probe is mechanically loaded into the said surface of the other part and is responsive to positional changes between its tip and its housing to provide an output signal for changing the drive motor speed.
The result is that the width of the weld groove has been automatically and continuously monitored and compensated for.